Take a look at the two images below. Can you tell which one has a message hidden within it?

Even though it is impossible to notice, the image on the left has a hidden text file in it. The hidden message says:

“This is a test file used in my steganographic encryption fun.

http://infosecstuff.com”

I created the text file using Notepad, and then used a tool called Steganos to embed the text file within the image. This is an example of steganography, one of the most fascinating fields of cryptography.

Steganography is not anything new. In fact, it dates back thousands of years. The ancient Greeks and Romans would often hide messages that they did not want to be intercepted using various means. In more recent times, steganographic techniques were used during World War II. And it is believed that terrorists use this method today to communicate messages securely. Basically, steganography is the hiding of messages such that the presence and contents of the message cannot be detected or revealed. In the digital age, it has come to mean the hiding of messages usually within image, sound or video files.

So how does this work? Steganographic tools take advantage of the fact that the least significant bit (LSB) of a binary file can be changed without altering or destroying the file significantly. In fact, many other security techniques such as hash functions and checksums also manipulate the LSB for their purposes. The file you are hiding must be smaller than the one you are using to hide the message and it works best for small messages. Larger hidden messages can result in the distortion of the original file which will make it easier for others to detect the hidden message.

Steganography has many applications including digital watermarks and the protection of private information. But it can also be used for fun and cool home projects. Here is a clever example of using steganography as a party sign or even a home decoration by my colleague Bob. How cool is that!